The present invention generally relates to the field of extracorporeal blood processing and, more particularly, to methods and apparatus which may be incorporated into an apheresis system useful for blood component collection, or for therapeutic purposes.
One type of extracorporeal blood processing is an apheresis procedure in which blood is removed from a donor or patient (hereafter, donor/patient), directed to a blood component separation device (e.g., centrifuge), and separated into various blood component types (e.g., red blood cells, white blood cells, platelets, plasma) for collection and/or therapeutic purposes. One or more of these blood component types are collected (e.g., for therapeutic transfusion purposes), while the remainder are preferably returned to the donor or donor/patient.
A number of factors may affect the commercial viability of an apheresis system. One factor relates to the operator of the system, specifically the time and/or expertise required of an individual to prepare and operate the apheresis system. For instance, reducing the time required by the operator to load and unload the disposables, as well as the complexity of these actions, can increase productivity and/or reduce the potential for operator error. Moreover, reducing the dependency of the system on the operator may lead to reductions in operator errors and/or to reductions in the credentials desired/required for the operators of these systems.
Donor-related factors may also impact the commercial viability of an apheresis system and include donor convenience and donor comfort. For instance, donors typically have a limited amount of time which may be committed to visiting a blood component collection facility for a donation. Consequently, once at the collection facility the amount of the donor""s time which is actually spent collecting blood components is another factor which should be considered. This also relates to donor comfort in that many view the actual collection procedure as being somewhat discomforting in that at least one and sometimes two access needles are disposed in the donor throughout the procedure.
Performance-related factors continue to affect the commercial viability of an apheresis system. Performance may be judged in terms of the xe2x80x9ccollection efficiencyxe2x80x9d of the apheresis system, which may in turn reduce the amount of donation time and thus increase donor convenience. The xe2x80x9ccollection efficiencyxe2x80x9d of a system may of course be gauged in a variety of ways, such as by the amount of a particular blood component type which is collected in relation to the quantity of this blood component type which passes through the apheresis system. Performance may also be evaluated based upon the effect which the apheresis procedure has on the various blood component types. For instance, it is desirable to minimize the adverse effects on the blood component types as a result of the apheresis procedure (e.g., reduce platelet activation).
The present invention generally relates to extracorporeal blood processing. Since each of the various aspects of the present invention may be incorporated into an apheresis system (e.g., whether for blood component collection in which xe2x80x9chealthyxe2x80x9d cells and/or plasma are removed from the blood or for therapeutic purposes in which xe2x80x9cunhealthyxe2x80x9d cells and/or plasma are removed from the blood), the present invention will be described in relation to this particular application. However, at least certain of the aspects of the present invention may be suited for other extracorporeal blood processing applications and such are also within the scope of the present invention.
A typical apheresis system which may embody one or more aspects of the present invention would generally include a blood component separation device; for example, a membrane-based separation device and/or, a rotatable centrifuge element, such as a rotor, which provides the forces required to separate blood into its various blood component types (e.g., red blood cells, white blood cells, platelets, and/or plasma). In one preferred embodiment, the separation device includes a channel which receives a blood processing vessel. Typically, a healthy human donor or a donor/patient suffering from some type of illness (collectively referred to here as a donor/patient) is fluidly interconnected with the blood processing vessel by an extracorporeal tubing circuit, and preferably the blood processing vessel and extracorporeal tubing circuit collectively define a closed, sterile system. When the fluid interconnection is established, blood may be extracted from the donor/patient and directed to the blood component separation device such that at least one type of blood component may be separated and removed from the blood, either for collection or for therapy.
When the blood processing vessel is loaded into the channel, the blood processing vessel and most of the tubing lines must be primed. In this regard, an aspect of the present invention relates to priming these elements, preferably with blood. A channel associated with a channel housing, which is rotatably interconnected with a centrifuge rotor, preferably includes a first cell separation stage. The channel extends generally curvilinearly about a rotational axis of the channel housing in a first direction. The channel preferably includes, progressing in the first direction, the first cell separation stage, a red blood cell dam, a platelet and/or a plasma collection area, and an interface control region for controlling a radial position of at least one interface between red blood cells (RBCs) and an adjacent blood component type(s) (e.g., plasma and/or a buffy coat of white blood cells (WBCs), lymphocytes, and platelets). Blood introduced into the channel is separated into layers of red blood cells (and/or a buffy coat generally including white blood cells and platelets), and plasma in the first cell separation stage. Preferably, throughout an RBC/plasma apheresis procedure (e.g., a non-platelet procedure) and including the priming of the blood processing vessel, only separated plasma flows beyond the red blood cell dam where the plasma may be removed from the channel in the plasma collection area. This is provided by an interface control mechanism which is disposed in the interface control region of the channel and which maintains the position of the interface between separated red blood cells and the plasma such that this condition is maintained. Note, the buffy coat (platelets and WBCs) is also preferably kept behind the RBC dam in the RBC/plasma collection procedures. In this embodiment, the buffy coat is generally collected with the RBCs and may be either later filtered out (e.g., the WBCs by leukoreduction filtration) or left in the RBC product (the platelets).
Although the term xe2x80x9cblood primexe2x80x9d may be subject to a variety of characterizations, in each case described herein, blood is the first fluid introduced into the blood processing vessel. One characterization of the blood prime is that separated plasma is provided to the interface control region before any separated red blood cells would ever flow beyond the red blood cell dam into the plasma collection area. Preferably, no RBCs ever flow over the RBC dam. Another characterization is that blood and/or blood component types occupy the entire fluid-containing volume of the blood processing vessel before any separated red blood cells would flow beyond the red blood cell dam into the plasma collection area.
A further aspect of the present invention relates to blood priming an apheresis system which includes a channel housing having a blood processing channel associated therewith, a blood processing vessel disposed in the channel and which has a blood inlet port and a red blood cell (RBC) outlet port which also acts as an interface control port. The RBC/interface control port is used to control the radial position of at least one interface between separated red blood cells and a blood component type(s), here preferably plasma, disposed adjacent the separated red blood cells.
Another aspect of the present invention relates to the RBC/control port which assists in automatically controlling (i.e., without operator action) the location of an interface between the separated red blood cells and the separated plasma relative to a red blood cell dam in the processing vessel. The red blood cell dam restricts the flow of separated red blood cells to a plasma collect port. The RBC/control port extends through the blood processing vessel and removes plasma and red blood cells as required in order to reduce the potential for red blood cells flowing xe2x80x9coverxe2x80x9d the red blood cell dam to the plasma collect port. The capability of xe2x80x9cselectivexe2x80x9d removal of red blood cells from the blood processing vessel through the RBC/control port is based at least in part upon its position within the channel. That is, the automatic control provided at least in part by the control port is predicated upon the control port assuming a predetermined radial position within the channel. In order to facilitate achieving this predetermined radial position within the channel, the disposition of the control port is provided independently of the thickness of the blood processing vessel. Specifically, the position of the control port is not dependent upon the thickness of the materials which form the blood processing vessel.
Another aspect of the present invention relates to a packing factor associated with the separated blood component types in a separation stage of the blood processing vessel. The packing factor is a number which reflects the degree with which the blood component types are xe2x80x9cpacked togetherxe2x80x9d in the separation stage and is dependent at least upon the rotational speed of the channel housing and the flow rate into the blood processing vessel. The packing factor may be characterized as a dimensionless xe2x80x9cdensityxe2x80x9d of sorts of the respective blood component type in the respective separation stage. One embodiment of this aspect is a method which includes the steps of rotating the channel housing, providing a flow to the blood processing vessel in the channel housing (e.g., the flow includes blood and typically anticoagulant as well), separating the blood into a plurality of blood component types, and adjusting the rotational speed of the channel housing based upon a certain change in the flow rate. Since the packing factor is dependent upon the rotational speed of the channel housing and the flow rate into the blood processing vessel, the methodology of this aspect may be used to maintain a substantially constant and predetermined packing factor. In this regard, preferably the packing factor is maintained between about 11 and about 15, and preferably about 13 for collection of RBCs alone and preferably about 16 for collection of RBCs contemporaneously with plasma.
A further aspect of the present invention relates to the extracorporeal collection of both or either plasma and red blood cells utilizing the same blood processing vessel. More particularly, such a method includes flowing blood from a donor/patient to a blood processing vessel and separating plasma from the blood within the blood processing vessel. At least a portion of the plasma is collected in a collection reservoir that is separate from the blood processing vessel. Further, such a method may include separating red blood cells from the blood within the blood processing vessel and collecting at least a portion of the separated red blood cells within a red blood cell collection reservoir that is also separate from blood processing vessel. In one approach, the collection of plasma and red blood cells may be advantageously completed contemporaneously, although they may also be collected during separate time periods. For example, plasma collection may be completed prior to red blood cell collection. Alternatively, red blood cell collection may precede plasma collection. Note, in a continuous apheresis process, the steps of separating and collecting may be performed substantially simultaneously.
In conjunction with this aspect of the present invention, and prior to the step of collecting red blood cells, the method may further include a set-up phase during which a desired packing factor is established within the separated red blood cells in the blood processing vessel and a desired AC ratio may be established. Preferably, such a packing factor is established to be between about 11 and 21, and most preferably at about 13 for collection of RBCs alone and 16 for collection of RBCs contemporaneously with plasma. Further, it is preferable that the AC ratio be established to be between about 6 and 16, and most preferably at about 8. The method may further include removing blood from a donor/patient and returning uncollected components of the blood to the donor/patient via use of a single needle. Such removing and returning steps may be alternately and repeatedly carried out during blood processing, including during the set-up and collection phases for red blood cell collection. If the collection of plasma alone is desired, the method may further include separating plasma from the blood within the blood processing vessel and collecting at least a portion of the separated plasma in a separate plasma collection reservoir. Most preferably, plasma separation/collection may be completed contemporaneous with the separation/collection of RBCs. Alternatively or additionally, plasma separation/collection may be completed before or after the separation/collection of RBCs. The use of a replacement fluid is also contemplated during collection and/or may be used in a substantially continuous (including cycled for single needle draw/return alternating applications) or in a bolus form.
Moreover, another aspect of the present invention involves the presentation of versatility in providing virtually any option for the collection of red blood cell, plasma and/or platelet products. More specifically, the present system can be operated such at that upon input of the donor characteristics (e.g., height, weight, hematocrit and platelet pre-count) the present system will return a list optional donations this particular donor can provide. For example, with a sufficient total blood volume (calculated by the body height and weight, e.g.) and hematocrit and platelet pre-count, a donor can produce possibly several alternate and/or a plurality of products; and, the system can determine not only how many and what combinations of products this donor can donate, but also what might be preferred or prioritized by the blood center. A sufficiently large donor may produce one or more red blood cell products and one or more plasma products and/or one or more platelet products. Many variations of product combinations may now be realized. Different tubing and bag set options are also preferably presented for such alternative collection procedures.
These and other features of the present invention will be made manifest by the detailed description and the attached drawings which are intended to be read in conjunction with each other as set forth below.